I'm considering it, Ted.. I've priced the Sola-tubes, installed, with several local companies and they were all in the $800 price-range.. I did, however, find one company who would do it, all included, for $600..
The key to the project, I feel, is good southern exposure, and the ability to make the tubes as short as possible.. My problem is I can get the southern exposure, but my tubes in the atttic will end up being like 10' long.. and then 3' more coming from the ceiling to the tank.. So I'm thinking I would have to go to the 8 or 10 inch diameter tubing, which means bigger holes in the roof..
There are a few good threds with pics on RV.. One guy has a 600 or so gallon tank with 3 18" tubes.. Also had some VHO or T-5 for actinic and it looked fantastic.. Somewhere in the thread he talked about the fact, too, that there is an equally neat effect in the tank at night because you get the true cycling of the moon...
All in all, I think I would be up for it if I could find someone with experience to help me install them; to keep costs down.. But the trouble will be convincing my wife that it's safe to cut huge holes in the roof..