Having got a Mardave undertray, I wanted to install it on the top without the complete tray being fitted. So having a think, I remembered the TRF503 using the TRF511 undertray but we had to cut them down.
So this is what I did. I cut the Mardave undertray in half and then trimmed it to fit under the battery boxes....
I will also use double sided tape to stick the sides to the chassis. This will then firm the sides up and I can then install Velcro to firm up the body sides once fitted. This should then stop the flapping around of the tray and body....
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