I always make my own trays from
ABS electronics boxes from Radio shack. About $5 and quite sturdy.
You do need to do a bit of work, namely remove the screw standoffs from the inside (for mounting the cover, which you will not need) then a couple cuts thru the plastic lengthwise to trim the width down (this is nice so you can make custom sizes.) I cut them down in a way so there is a lot of overlap, for which you apply black ABS cement ($3 from plumbing section at hardware store,) press together, let dry 15 min, then trim down height w/ a saw (whatever you need) then they are basically ready to install into chassis. I add a thin layer of batt tray foam as well.
On trugs I countersink flathead screws and mount directly to chassis. I mount straps over them, directly bolted to chassis. The trays are extremly durable and tough. ~1/8" ABS. Never have broken one yet, and can be made to be very protective of the lipo.
Here are two mounted in the hyperSt and the .5:
