I found some time to try to install the panel + counter extension.
First since I had everything at home I carefully measured and put it together:
I used the clamps to hold the front panel in place--I couldn't permanently attach it because I wouldn't be able to install it into the RV.
Looks like I'll be just fine (I measured just under 2" of room between the door and the panel).
Panel installed with some extra screws--thank you Thor for leaving me some screws lying around for just such a project (also note the extra reinforcing dowel for the hinges).
All installed. The new panel is glued into place and currently held on using Thor's best practice: staples--I only used a few and given where it is no one will ever notice them.