The best option is to have friends or family with backup locations of their own, that are equally viable for long term survival. So, say your place gets destroyed in the initial event, but Uncle Bob's farm is a hundred miles away, and has plenty of extra room, water and food, too. Then you just need to get yourself to Uncle Bob's place and you're good to go.
Even if you don't have a circle of like-minded survivalist type friends/family in the region, it's good to know have an idea of where you could turn for a safe place to sleep and regroup, even if just for a short while. We have friends who lost their home in a tornado a few years back, and they ended up living with some family friends for a few weeks while they located a new place to live and regrouped from the devastation caused by the storm. It never hurts to have these conversations beforehand - and if you're the prepared party, extending an invite to trusted but potentially less prepare parties can be wise.
Post-collapse, you'd see lots of friends and family "holing up" together to share the workload and improve odds of survival. Same reason that families in the old days used to be big and multi-generational in the same household - it made sense for survival.
Now you may have no where to turn to, Uncle Bob's survival cabin may be compromised, and your other options no-good--your friends/family in suburbia may be in the same or worse lot than you will be. So, then what?
Squatting in an abandoned home may be a viable option - if the owners are most likely dead and the home sitting wide open, then why not? There are of course risks involved (what if the owners aren't dead and return to find you've invaded their home), and there are a great many situations where holing up in a seemingly abandoned home/building may not work out so well.
So, it can pay off to have some variety of durable long-term but still portable shelter as a "go-to" option. Here's a run-down the main options as I see 'em.
Modern Recreational Vehicle
An RV or trailer comes to mind as the modern solution, with the conveniences of home. They'll on conventional fuels like diesel and propane to keep those modern conveniences running. You'll also typically be limited in your mobility, though there are some fairly off-road capable models out there - check out Expedition Portal to get you started. If you can drive to a safe enough hidey hole and set up shop, a modern RV or trailer plus an ample supply of fuel has a lot going for it. One could certainly pre-position buried fuel tanks and other supporting infrastructure at a retreat, and bring the trailer/RV when the balloon goes up - certainly less expensive then building an entire home. Also, compared to the other options we're looking at, you've got a lot more storage capability and can haul along a lot more gear - if you can drive it there.
Downsides: Cost is a big one - you're looking at thousands of dollars, especially when you start looking at off road capable stuff. Some models will fare with bad weather and winters better than others - many are going to have a tough time getting through cold weather. Nearly all are going to be designed around the availability of fuels to keep heating, air conditioning and other conveniences going. Reliance on roads is going to inhibit most models, too.
A poor name for the category, but this includes heavy shelters that are too large and heavy for one person to carry in a pack and will require pack animals or an off-road vehicle to carry. Wall tents, tipis and yurts are example here. These were made for a time before modern luxuries like heaters or indoor plumbing. They will use a wood stove or fire pit for heating in cold weather. People have lived in these long term for years on end and the heavy duty materials are meant to last.
Downsides: Cost - a good wall tent or yurt is going to be a thousand dollars on up, plus a stove. And you're going to need help with transportation - horses, an ATV with trailer, etc.
A typical backpacking tent is not made to last through long-term use in rough conditions, but there are some ultralight tipis on the market intended for extended trips in nasty weather. They use titanium stoves to heat the shelter during winter conditions, and the tipis are made from special technical fabrics to maximize the square footage for the given weight. They're certainly packable by one person. Kifaru and Seek Outside are the two brands that I've seen get the most press.
Downsides: Cost - again - though you can get into a tipi and stove for under a thousand without too much trouble. Durability is going to be a concern as well.
Shelters made from natural materials with basic tools - how people lived in the old days. There are a myriad of options here - from a hewn log cabin to a wikiup - and, built right, they can do very well in a long term survival situation. Mankind has lived in shelters of this sort for most its history, so they're certainly viable (if a bit cramped, dark and dirty). Most can be built with only simple hand tools - a knife, saw and axe can do a lot in the right hands. And of course, if you have the natural resources, you only need the tools, calories, time and knowledge to build one. Otherwise free and the tools can go wherever you go.
Downsides: Requires calories, time and knowledge to construct - time and energy that may be wasted if you have to relocate soon after. Will often require more maintenance/upkeep than other options, too.
The best bet would, as usual, to layer one's options - an RV and a packable tipi, plus the knowledge of how to build a handful of primitive shelters, for example. Primitive shelter is the baseline - if you can build a solid primitive shelter from natural materials available in your region, you should be able to keep shelter over your head no matter what happens.
I don't have a ton of expertise/experience living out of any of these shelters, and I'm sure there are some of you have have lived in any/all of them, long term. Interested to hear your thoughts/experiences in the comments!