The cargo tray link you shared has a picture of a Casita
in the photos. :-)
We put our Stromberg cargo tray on a Scamp
16 and it's a lot easier to lift the bikes onto the cargo tray, than to lift them onto the top of the tow vehicle.
We used our existing bike carriers that went on the tow vehicle crossbars, and mounted them onto the cargo carrier.
No problems with opening the back of our truck, but on our Dodge Durango SUV we need to make sure we are parked straight in front of the camper if still hitched so the liftgate clears the rack by about 2". (If we use a curved pull-through and the SUV is at an angle and still hooked up the liftgate will hit the rack).
There are many adjustments so you should be able to find a position that works for you.
You do need to keep an eye on the weight like you mentioned. Our tongue weight with two bikes went up to 440, which is OK because all our tow vehicles have higher limits, plus our loaded Scamp
comes in about 3,000 pounds so that works out to a little less than 15%.
No problems with pulling, or backing into campsites, but you definitely want to check to see what clearance you have during tight backups