We've got a Keys 7-person which was basically un-insulated, and our electric bill ran about $60 higher per month in the winter after it's installation (upstate NY - 13084 zip-code for weather info).. Just finished insulating it yesterday, and am curious to see what the impact is.. If you live in a cold-weather climate I'd suggest poking around under the tub to see what you've got for insulation. I added 1.5" foil-faced foam board to bottom and sides, with Reflectix applied as a "curtain" across the bottom and around the sides (inside of the 2x4 frame), and ensured air-space between the foam board and reflectix - then taped the seams between foam boards, and applied Tyvec house-wrap around the exterior before re-attaching the side pieces. Had to remove the 3/8" plywood blocking that was attached to the inside of the side pieces to get them to go back on.. Entire job took just over 8 hours, and cost around $200...
