Karlton,
I'm not sure how new your Hawk is, but my thinking is that there are actually two issues at stake here: 1)proper fitment and 2) water evacuation under the camper bed to prevent rot.
If you have a newer Hawk, #2 is a moot point because, it appears to me, that FWC engineers have decided to run uniformly spaced planks across the camper belly in recent models. I haven't seen one of these in person so I don't know what the depth of these planks are (maybe 1/2-5/8"?) but this change in models must be to create space to allow for water evaporation under the belly. Moisture pools in the open spaces under the wood and then it evaporates, something it can't do if it is trapped under the wood. If you already have one of these models, then I don't have much to offer except to repeat the advice of others using a platform.
If, however, you have an older model, I would go find one of the new models and find out the exact measurements of these slats and mimic the depth and spacing as close as possible with your camper, but enough so that it gives you the bare minimum of elevation to clear the rounded tailgate opening. Maybe give yourself an extra 1/4" to allow for wood shrinkage or compression over time. Maybe some of the synthetic decking material would be better even. But this method would not only fix your problem but also add an innovative feature that FWC has decided (I'm sure with good reason) to include on all new models.
This is something I hope to eventually do on my own renovated Keystone some day. I've with mechanical engineers my entire career, and one thing I've learned is to respect the engineering that goes into a well-proven manufactured structure. So I try to stay as close to it as possible, when possible.