Top mount for rear airsprings (trailing arm)

[panhandler62]

I'm mocking things up and I see that my bags center up in the frame (and c-notch re-enforcing plate!) real well, which is more likely attributable to Nathan Porter having made the trailing arms correctly than anthing I did.. lol

What I want to check before I move on is if I need a mounting plate on top. The bags are wider than the frame section. They frame section is very heavy here (thanks to the notch plate) so I'm not worried about it buckeling but I thought I should ask y'all if it's ok to simply bolt (and plumb) them through the frame or if I should make a plate (w/wo gussets?) that covers the entire width of the bag.