Consider 2 pairs of these GRP Park Tires:
http://www3.towerhobbies.com/cgi-bin...?&I=LXMXW1&P=0. They use firm molded foams that have very little ballooning. They are mounted truer than any set of tires I've ever mounted myselft and glued very well too. For $16.50 a pair and pre-mounted you can't loose.
They come in the Associated T4 offset that works perfect with the crt.5. I don't think it has quite as much offsett as the traxxas rims, but they don't have any clearance issues. They do use a pin mount, but I've had better luck with the pins than the hexes. You do have to shorten your pins about 1mm.
E-CRT.5 Monster - RCM chassis, MM/Medusa 50x3300/3s, truck tires, 1/8 shocks
E-CRT.5 Stock - Sidewinder/4600/2s, buggy tires
E-8ight - Tekin RX8 2000kv/4S
E-8ight T- Tekin RX8 1700kv/5S