I believe all of the (newer, at least) RW kits are thin-wall FG. My Go Devil 38 definitely is. In fact the thin-wall fly-away guide is still a loose fit on my Go Devil 38, I still had to shim it to make it a good fit.
On the shimming, I would definitely have to side with rubber bands. The first time I used some carefully-cut pieces of duct tape for the shims, and that worked well (and is certainly more fine-tunable than rubber bands) the first event (two flights), but I can only guess that while sitting a month (mid-September to mid-October) for the next event the tape must have shifted a bit and left some tacky surfaces, my next flight the guide didn't come off until apogee, which both resulted in a much lower flight than expected (that was my first attempt at breaking a mile and it wasn't even close) but also resulted in the loss of the guide (never found it on the field, don't even really know just where it would have come down). I will note that Bill replaced it free of charge which was totally unexpected. Now I'm using rubber bands, all I had the first time was the supplied bands and they still weren't quite thick enough for my Go Devil and the thin-wall guide, so I put some blue tape between the guide and the rubber band, at least this is spaced away from the airframe so it shouldn't have a chance to stick. I still need to buy an assortment of bands to have more choices on thickness (and not be chewing through the supplied bands which are perfect for the guide release).
I shoot to have it a fit snug enough that you can grab the rocket somewhere other than the guide, move the rocket up/down on the rail and have the guide stay in place on the rocket. This was tricky my first event, what seemed right off the rail didn't slide on the rail at the pad, I believe it was due to the screw heads grinding against the inside "V" of the 1010 rail (all of my other rockets use countersunk screws so this wouldn't be a problem with them, the pan heads on these guides seem very large to me. But I wound up removing a strip of tape at each end which was just about at the tipping point between rail-to-guide friction and guide-to-rocket friction. But it flew well every time, I'm on my 5th flight with these guides (this past Saturday I finally did my mile shot successfully) and there's not so much as a mark on my fin fillets / etc.