OK, here's the deal: So I'm probably getting hermit crabs but I was thinking, I really don't feel like spending a bunch of money on a new big tank, especially because I already have a couple at home that would be suitable for them. I did some research because I want happy hermies and want them to be healthy and not miserable, but I learned that it would be best to get a tank that is at least a few gallons. This is a problem because the ones I have are 2 gallons at most and that doesn't give them much room, so I thought... Why not combine them? I mean I have 3+ tanks from when I had fishies and it couldn't be that hard right? It's not like there's going to be water in there, only sand. And if I combined 2 together it would give them enough room to climb around and stuff. I'm only going to get 3 hermits at most, maybe 2. But I have 2 kind of big problems, though. First of all, how am I going to do this? How do I cut it and seal them back together? I'm not very handy but I do have the tools. Second of all, hermies need humidity and heat and stuff. The tanks have small heaters in them which is good. So since I need to heat the tank(s?), I can't just cut off the side walls and then glue them together because the tops of the tanks wouldn't fit. I was thinking I could cut off a section but not the entire wall so that I can put both tanks side by side and it would be easier. If this is too confusing please tell me and I'll try to explain it better. Is it worth it? Would this even work?? Thanks! Please help...

I find it useful to watch how others have done projects such as yours and here is a pretty good video.

https://www.youtube.com/watch?v=mPzMbyQjil4

More on removing the glass panels

https://www.thespruce.com/making-glass-aquarium-repairs-2920653


Take a razor blade and run it between the panes of glass to sever the silicone, and completely remove the pane. Be very careful and don't rush this step, and do not try to pry the glass pieces apart. Allow the razor blade to do the job, just working at it until the pieces separate pretty much on their own. Glass breaks very easily when pressure is put on it, and the edges can chip, making your repair job a much larger task if the glass gets damaged.

The way I see it, attentions should be especially paid to the foundation support since combining aquariums together to make your crab terrarium will be weak where they are joined and make moving lifting a real challenge.

Not a lot of videos to be found, but I suggest laying everything out on paper first (A plan, including a list of tools and materials)) before you get started, as well as review a few glass replacement techniques and methods just to get familiar with this tedious process.

Also aquariums are generally sealed with silicone, and though you have no worry about leaks, I would stick with that as a sealant, just in case you get the notion to go back to fish. Have fun and let us know how it turns out.

Note.

You can also shop around for reasonably priced 10 gallon tanks. that

I wouldn't try it if you're a novice and not that handy, unless the materials you're buying aren't that expensive.

Do try looking at a local buy and sell group in your area, or a thrift store. Every tank I've ever had, smallest was 10 gallons, I've gotten for less than $10 used. The last one even had a lid perfect for our gerbils. Since you don't need a water proof tank you should be able to find a used one for cheap, probably cheaper than what you'll spend trying to make your own.