Mustangtyson,
I guess that there are a few ways to do this:
1. Place your tanks next to the wall and chain them there. I know a lot of guys who have done that who didn't need to move their tanks.
2. Be patient and find a used, industrial quality one at an auction or CL.
3. Build your own cart, if you have access to a welder & steel. The black one pictured below is one I built years ago (I used a ratchet strap to secure the tanks). The grey one is a cart that I flipped. I'm sure that others here have good ideas for building your own.
4. If you need one NOW, shop for a new one. Harper hand trucks look good. I'm sure that there are others. I've looked at HF carts, and I'm not impressed, although they may be fine for hobby use.
IMO: I wouldn't bother with the firewall. I assume that you do all of the normal safety practices (shut off valve & empty hoses when done, etc). However, I would strongly recommend investing in a set of flashback arrestors, if you don't have them.
Let us know what you find.
In my situation: I'm in the process of "rebuilding" my oxy/acetylene set. I also need a cart. However, I plan to just keep the tanks chained to the wall until I find a cart at an auction. I currently don't have the steel to build one. The hunt will be a little longer for me because I'll need a cart with a 400# capacity.