Welcome, Brian! We have a PT52, and love it!
Adding diesel heat is an easy DIY project- you just have to get comfortable with the idea that you'll be boring holes in the boat. This project can be done in your slip. I just installed a Wallas 40DT heater on our boat- it's quiet, and keeps the boat wonderfully warm!
Adding A/C usually requires at least 1 day out of the water to drill the hole for the seawater inlet. It's a bit more complicated, as you're dealing with fluid systems as well as air systems. Again, depending on your skill level/bravado level, it's not a hard project to complete.
Peter- Marine Insurance Guru & tuna fishing addict!
1989 52' PT Overseas yachtfisher