Why isn't X mod compatible?
As of v1.1.0, all vehicle mods should theoretically be compatible. There is a list of partially compatible, and fully incompatible mods on the main page along with explanations for these mods could not be made compatible. Any mods not listed there, that do not show equipment grids should be brought to my attention in the discussions tab.

Vehicle not displaying the correct equipment or grid size?
There is a list of fully compatible mods on the main page along with explanations for what equipment grid type they fall under. If a mod is not listed, then it may be new, and has not received specific compatibility; please post these in the discussions tab, tagged as Ideas & Suggestions. If the mod IS listed on the main page and appears to not be working correctly, then post it in the discussions tab, tagged as Bugs.

Overriding existing vehicle grids?
This (currently non-existent) feature would theoretically be used to add grid settings to vehicle mods which added their own grid, but didn't allow customization of the grid size. The only issue preventing the implementation of this feature, is that there is no easy way to tell within the code, if an equipment grid allowed for customization. So I would need to implement a blacklist (or conversely, a whitelist) to selectively allow modifications for only specific vehicle grids. This would take a bit of effort, and the payoff would be.. minor at best.
But I would be willing to add this feature, if there is request for it.