The rack is best used in a pickup with a cab height topper. Of course you wouldn't use it with a 5th wheel. My hybrid bikes are too tall to go in standing up.
The base is 3/4" plywood, 23-1/2" x 63". I could have made it several inches smaller each way, but larger is more stable. There is a small amount of wasted space behind and under the bikes that can be used for soft bagged luggage. About a foot of space to the right of the bikes needs to be cleared for access to the front mounts. I will pack the lighter, easier to move items there.
The idea of locking the bikes is good. I need to provide a method of tying down the bike rears to prevent them from lifting in a panic stop. Maybe I can incorporate a lock in that mechanism. I previously used Harbor Freight movers blankets on the bikes to protect them and the truck. I plan on continuing their use.
I need to add handles at each end of the base to make it easy to move. I also want to provide carpeted bumpers where the base contacts the truck bed. The base would probably never move on the rubber mat, but I will provide positive attachments anyway.
Yes, Photobucket is miserable.