If comfortable was my requirement, heavy or not, it would be a shoulder holster. I'm 5' 11" and 218# and iwb is uncomfortable because I'm kinda short-waisted. CZ 75 pokes me in the bottom rib. Murse goes with me most days. OWB about 4 o'clock if I need hands free.
Chainsaw 2 flats at opposite edges. Looong lag screws through 2x8s. Then some 2x4 joists on top. Or just a 4x6 sheet of marine plywood. Go up from there.