I installed an Inferno Maxx heater into my 3 seater. I dont have all of the vents plumbed up, as of yet, and it keeps me pretty warm already!! If you are even somewhat handy, I highly recommend the Inferno and Inferno Maxx heaters (250 cfm vs 350 cfm, iirc)
Stay warmer outside longer with a top-quality Honda Pioneer 1000 Cab Heater with Defrost for 2016-current models from Inferno Cab Heaters.
infernoheaters.com
Stay warmer outside longer with a top-quality Honda Pioneer 1000 Cab Heater with Defrost for 2016-current models from Inferno Cab Heaters.
infernoheaters.com
I use mine for pipeline work, and I do most of my own work and mods, this install is not too difficult at all, heater sits under the driver seat. I have a plan to change my heater ducts for the windshield, I am looking at fabricating a pvc duct to go across the lower windshield. Tees for the inlet and the outlets. I have vents already in the seat sidewall, right behind your legs. Still in the planning stage, but I think I can make it work very well, just to share an idea. Anyways, as far as sealing your cab, you can get thick rubber sheeting and make seals to overlap gaps, or even use some spray foam to seal gaps that do not flex (be careful as the foam expands lols, but you can trim it back, use tape to build a wall and spray foam in the gap. You have huge gaps under the hood, in the inner front wheel wells. Super ATV makes a part to help seal it from mud, which you can then seal from wind also:
Also, there is a mod where people use a boat bilge pump to blow out excessive heat from the motor and transmission under the seat out the bottom or back of your buggy. Some people have plumbed that up to also be able to blow that hot air into the cab during the cold season. Hope some of this helps you out.