you need to read more about towing specs.
first, that trailer is nearly 30'!!
second, your Flex's 4500lbs. tow capacity is with only a 150lb. driver in it. any additional passengers or cargo, lower the 4500 by its weight, including the WDH's weight.
the trailer has a fictional "dry" weight of 4050lbs. this does NOT include the weight of so-called "options" that nearly all trailers have, such as:
awning, oven, a/c, spare tire, microwave and so on. so, a ballpark number would be to add 400lbs. to the "dry" weight, to get the actual weight from the factory. so, expect it to weigh very close to your 4500 max.
now, you still have to add the weight of the battery, propane and water before you even try to add the weight of the cargo.
third, the "dry" hitch weight of 410lbs. will easily be over the Flex's max tongue weight when loaded for camping.
bottom line: too long of a trailer, too heavy of a trailer and too much hitch weight.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC