I built a few things for my Rover 1.5 that have been very useful to me. Some of my mod's are posted in other threads, and since my comp crashed last night, I can't upload pics right now. but I've built;
Auger Rack - on the outside of the sled. no more carrying the auger, and not worried about it tearing material or bouncing around on top of gear.
Tackle "Caddy" - can be seen here..
http://www.iceshanty.com/ice_fishing/index.php?topic=214520.0Adjustable rod holders.
Also built an aluminum framework/divider in the sled to hold my bait bucket, heater, a spare pail in place.
Added a longer rope to the sled and ski's, pulls much nicer by hand.
For lighting I thought about wiring in LED's but instead of that, I bought 3 rechargeable LED treble lights. cheap, very bright, they last for hours, magnets hold them in place on the frame rails on the sides or ceiling.
If your not familiar with the rover 1.5 for seating, all it comes with is a carpeted 2x6 for a "bench" I added a nice padded folding stadium chair, and that was okay for a while, but I'm working on idea's for better seating as well. Also looking into insulating.
Good luck!