I have a 1994 600 series Sundance that is in need of some serious repair after a feeze out last January.
I am to the point where my remaining leaks appear to be on the underside plumbing.
I believe my next move would be to tip the spa onto its side (somehow) to access the bottom plumbing.
Anybody have any experience with this?

Yeah, if you need to then that's the easiest way.

Just be sure to put some carpet or something to prevent damage to the shell lip.

I have the same issue with my Sundance cameo, 1995.

after I rebuilt the pump wet ends (seals) and replaced a few fitting this Fall, I believe my water leak that it always had has gotten worse. May have waited too long with it empty to fix the seals.... :0

I think it is in the footwell. It has rotted out the lower structure of the wood frame, so I am gonna rebuild that when I tip it to repair the leak.

Any guess how heavy it will be?

I am going to refill it when it gets warmer....and use some common household laundry dye to "see if it stains were the leak is (on the foam on the outside of the tub). The shell is garnet marble colored, and the plastic is faded, so a Red residue from the dye job is no biggie.

I don't have a problem removing the motors/wet end (already did it when I found the leak had gotten worse before the Ohio winter), I also can remove the control box and blower assembly.

My plan is to tip the tub completely over and dig out the foot-well foam, where I think the leak is (supposedly common area to leak). If I can find the bad PVC (it's probably the glue as I have had to replace a few pieces already because of it), or jet fitting, I will build a frame, tip it back and refill to check for leaks.

If i fix the leak, I'll tip it back up, refoam, and put it back.

Does anyone have any diagrams of the Sundance 600 tubs (showing the foot-well plumbing)?

Thanks
DG