I think the CF straps are designed to fit a very specific length of battery tray since they attach on top of a post either end & are secured with a body clip- chances of the FLM chassis having the same holes in exactly the right places is remote.
As for the velcro straps, they were nothing but overpriced regular straps with the GorillaMaxx logo silk-screened onto them- paying $20 for a couple $2 straps is crazy ( probably why I have 4 on my GMaxx
). A much cheaper and stronger option is to make your own straps using something a bit more heavy duty, like so:
http://i115.photobucket.com/albums/n...Mulligan94.jpg
http://i115.photobucket.com/albums/n...Mulligan95.jpg
http://i115.photobucket.com/albums/n...Mulligan96.jpg
Very simple concept and lets you use any regular straps- you just need 2 per battery tray, quick google for 'battery straps' turns up loads of cheap options.