Looks good. The potential heavier tongue weight can be easily countered by storing more of your heavier stuff inside the trailer behind the axles. Use the bathroom scale method to help balance the load.
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Bill
2011 Dodge Ram 1500 HEMI Quad Cab
2011 Jay Flight 26BH
Are you storing the batteries inside the toolbox? If so then you need to make a provision for them to be vented. As batteries charge they give off hydrogen gas. It is toxic and corrosive and explosive in high levels. Look at the plastic battery boxes and you will see vents in the lids. I know west marine or other similar stores would have vents that can be installed over a cut out. I've had to do this several times on boats. Vent needs to high on the box. Gas rises and will dissipate on it's own. Just have to give it somewhere to go.
If you are concerned about added tongue weight , another box could be added to the rear bumper providing the bumper is strong enough. I tied my box on the bumper and tied it into the frame.
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Larry & Rachel Demers 2013 F150 Eco Boost Super Cab 6.5 bed 6 sp. 3.31 4x4 White Hawk 28DSBH