If you made up a table for a reciprocating saw and used a metal cutting blade, that may be your best option for closed interior cuts. https://www.mcmaster.com/saw-blades
I have a HF 4x6 that I've had for 30yrs. It's great in horizontal mode and can get by in vertical mode if you have it nailed down to something. If not and you really need to push on it, it's not stable. First thing I did was got one of the HF furniture dollys and mounted the saw to that. The legs are sheet metal. When I got tired of wrestling the 4x6 in vert mode I found a used 14" HF vert bandsaw and modded it to cut metal. When I need a metal cutting scroll saw I made a mount for my jig saw. It's actually easier for me to see what's going on because the blade sticks up through the work and I can see right where it's cutting. I also use a intermittent HF foot-switch for safety so I can have both hands on the work.