We can add Truxedo bed rails that will fit under your MX4 rails. The Truxedo rails will allow you to install racks or crossbars to your MX4. Just keep in mind that if you use low mounted rails, you won't be able to open your MX4 with the rails in place as there won't be adequate clearance. But it can be done!
If either of y'all are interested, please feel free to send me a PM and we can go over options.
Yup, Truxedo is what I was looking at using if I wanted to add one in the future. They'll fit nicely between the rails but I'm thinking I'll be good with the Decked drawers for dry/secure storage, and the space between the decked and the bottom of the rack I"m not too worried about.
Heard back from Frontrunner support today on the rails to confirm a few things:
Question 1 was about lengths: They only sell 1800mm rails that aren't predrilled. The magic number for our beds is going to be about 1675mm. Luckily they sell touch up paint so I'll be able to order the 1800mm rails, cut to size, and touch up the edge that's going to be closest to the cab.
Question 2 was confirming dimensions: True profile of the rails 45mm (1-3/4") wide by a very sleek 15mm (5/8") tall.
Question 3 was on clearance for mounting hardware: The rails are designed to be used with countersunk screws so there's minimal clearance between the legs and the track for hardware holding the rails down to clear. Sounds like this will be one thing I need to work out.
Nonetheless, Decked system comes tomorrow so that install will be this weekend. And I'll pull the trigger on ordering the Frontrunner rails to start that process as well!