Hey Raphael, I had the same problem but i found a bit a a solution, i added a v mount battery plate to the bottom of the rig. I got a the V-mount battery plate off ebay,
4x 1inch long 3/4 hex standoffs with 10-32 thread
4x 5/16 diameter 1/2in long spacers
https://www.google.com/search?q=5%2F16+diameter+1%2F2inch+long+spacers &tbm=isch&ved=2ahUKEwisqNuortjoAhXyJn0KHVB0CboQ2-cCegQIABAA&oq=5%2F16+diameter+1%2F2inch+long+spacers &gs_lcp=CgNpbWcQA1Dz9wJYqJoDYPSfA2gAcAB4AIABVYgB_AGSAQEzmAEAoAEBqgELZ3dzLXdpei1pbWc&sclient=img&ei=ooSNXqzPF_LN9APQ6KXQCw&bih=1076&biw=2133&hl=en
some 1inch long 10-32 cap screws and washers.
flip the rig over, take the thumb screws holding the sliding base on and replace them with the hex standoffs, then put the screws through the battery plate, put the washers and spacers on them screw the plate to the hex stand off. here's a good drive link to see how mine turned out
let me know if you have any questions. I got all the hardware stuff from a small hardware store, home depot didn't have it but a neighborhood ACE or smaller hardware store might.
good luck yo