This has got me wondering if part of the belts problem is bad fitting/placement on the part of the owner? If you two guys have had 18 months with no belts and 2 years with only 3 belts replaced you are doing smoething different (and possibly better!)
Likely to get flamed here, but just thinking out loud
How often, and in what conditions, did your cars get actually used in that 18 months and 2 years?
I reckon Im using my car more than most on here.
Im practising with my car almost
every day at least once a day (sometimes 2 or 3 times!).... and not a nice indoor safe carpet, but outdoors (gravel, tarmac, grass track) and all my races are again outdoors on dirt with some big jumps (its a 1.8th nitro track!!)
Time the car has run without belt changes isnt really the issue, its how much the car has been used (abused).
Im not trying to poke sticks, genuinely want to see if I can protect the belts better and maintain my car better.