Mike's trays are pretty solid from what I've seen if you want a pre-made solution. Otherwise, a custom aluminum tray works well if made right. Here is an idea of what I do for many of my conversions:
http://scriptasylum.com/bl_conversions/_hyper8.html
I use the velcro that comes on a roll. You can get it at Lowe's, Home Depot, etc. Just wrap it around the tray or bolt the ends. I've never had them let go before, but I try not to set up the tray where the velcro is load-bearing.