Can the SRV tow a tank?

Yes, it should be able to.

And can it tow it behind itself and basically make the tank into a spacefaring vehicle?

There would be nothing to stop that happening. Again, the tank, I believe it does have shield items on it, so they would have to be down. It's getting a bit A-Team, but theoretically there's nothing to stop that. The tank excels at ground combat. When you put a tank in space being towed by another ship, it loses some of its powerfulness.