There are several fluorescent bulbs on the market. I have used Thin-Lite since the mid 80's. Have had no trouble and see no reason to change. They are readily available at Camping World most RV Stores (www.thinlite.com/products.htm
1. A 2 bulb, 12" bulb length fixture will cover most incandescent fixtures for a nice fit.
2. Check the wiring of your incandescent. Most have the wiring coming from the center of the fixture. Buy a fluorescent fixture with the same wiring location. The fixtures are flush mount, and this is needed for smooth fit. You may have to enlarge the hole in the roof slightly to obtain the flush fit.
3. The 2, 12"flourescent bulbs will put out light equivalent to, or greater than 2 incandescent RV bulbs and use less current than the average single incandescent bulb.
My approach to light use while dry camping, which may not be accepted by all.
1. I use no generator,(I am there for the quiet) and have 2 12v group 24 deep cell batteries. Will consider going to 6v deep cell batteries on the exchange of these batteries.
2. Light conservation is essential. I use no incandescent lights. I try not to have more than 2 fluorescent lights on at a time. From this approach, I try to mount 3 fluorescent fixtures in critical use locations. This gives adequate light, though not excessive. Also saves money on fixtures. We spend time outside around a campfire and our eyes are adjusted to minimal light.
3. Try to do what needs more light before dark.
4. Remember that the fridge and water heater, possibly radio and clock, etc are using battery power while you are camping, and you have no choice on this use. LP Sensor is a hog.
5. If we get rainy nights and have to stay inside, we use fluorescent flashlight(s). May also use a lantern so as to not increase battery consumption. Lantern can be battery powered, or be sure to open vents if using propane/gas. Don't use gas if you don't know what you are doing!
6. Don't use TV battery for power source without running engine.
7. Carry good quality jumper cables to attach to RV power source if you have hydraulic slide/legs just in case you over use your battery power.
I learned my battery power/usage from an older TT that had fridge and water heater on gas pilots, no LP sensor, a propane mounted light (which we seldom used)and a single battery for power, and was able to dry camp for 5-7days. The above practices have allowed me to continue that type of dry camping with the extra battery power consumption of new "conveniences" . When connected to shore power you can mix fluorescent and incandescent lighting with no problem. Several of the new RV's have this mix as standard equipment.