It might depend on how your race is run on whether they would work for your race. Our Pack race is run by our local Boy Scout Troop.
The idea is to have at least 4 of these bins. 2 for the Starting / staging area and 2 for the finish. It essentially takes 4 people to run it (could take less or more). Basically, one person at the car table loading cars in the bins for each heat (they would have a printout of all the heats).
Once loaded in a bin it would be brought to the Scout staging the cars on the track (bins are color coded by lane). The scout staging the cars on the track would also have a copy of the heats to double check the right cars are being staged each heat.
One scout is at the finish area removing the cars from the finish into a bin. Another scout will be the runner bringing cars from the finish area back to the car table.
This should help efficiency and also ensure the cars are pretty well protected while being handled during the race. I'm sure there are a number of others that probably use a similar system, just thought I would post this as an idea people could take a look at.
The design uses 0.5" thick x .75" wide x 7.5" length Weatherstrip pieces (2 per car holder - 1.5" wide total). Then a piece of foam friction tape is placed on top of that to keep the cars from slipping around. Most, if not all, cars wheels should be off the bottom of the bin. If any cars' wheels do rest on the bottom of the bin I added foam pieces on the walls to keep them from being knocked against the walls of the bins (or at least make the bumps a little softer).