I've had a pretty stupid time with using Otter Wax on this bag I made, but I think it's my fault. Wax is just not an easy thing to work with when untrained and in unideal conditions.
Otter says to apply the wax, and then use a blow dryer and to work the wax into the fabric while it's hot. I tried this once on this bag, but I hadn't put on enough wax. Also I think I didn't use enough heat. You can't just point a blow dryer at a spot for a few second and then rub and move on like I did; I think you need to do it a few times. My bag was a. not particularly waterproof, b. pretty streaky, and c. still a little sticky.
So then, having left the house where there was a blow dryer I could use, I put more wax on the bag and then put the bag in the oven while it warmed up to get the wax to melt into the fabric a little better. Obviously, I couldn't rub it while it was in the oven, but when I pulled it out of the oven, the bag pretty much did not look waxed at all, which is weird, because I'd put a lot of wax on this time. I think I actually made the wax burn up or something. There's a spot or two on the bag that look legitimately waxed, and they don't feel waxy now. So the bag is now 5% waxed.
But thecow is right, and I hadn't realized before--Otter Wax does smell like Play Doh. I don't mind though. Don't know how it's gonna make all your clothes smell like wax unless you wax everything you own.
My short advice: Do it, but keep in mind DIY is always an experiment and often an adventure. If you apply wax and your garment isn't waterproof, apply more; if it's sticky, do more of the blowdryer+rubbing step. Don't use an oven.