Roof Top Tents - Is the mounting Dimensions all the SAME?

Gents,

I'm in the process of converting our boxtrailer to accept a RTT to it and was wondering if the bolt hole dimensions on the RTT is ALL THE SAME, no matter what Brand of RTT?

I haven't decided what brand to buy yet, but I'm wanting to make up a bracket to bolt the RTT to my trailer & I need to know if ALL RTT mounting holes are the same?

I've checked Darche and the 4WD SuperCentre (KINGS brand) RTT and it appears that the mounting is similar around the 830mm mark one way and also about 830mm the other way (square).

Would this be correct for all brands???

thanks in advance.....
rob