Truthly saying I have never experienced problems with crashes in eTrex 30.
Try to calculate shorter routes (max. 30 km long) and use less-detailed maps.
The only thing correlated with current FW 2.90 are bugs listed here:
http://forums.Groundspeak.com/GC/index.php?showtopic=308077&view=findpost&p=5220313
Nevertheless they should be mostly the same for eTrex 20 and eTrex 30.