Welcome
@slachlan. We're 20ft'ers, but the now highly collectable single-ended variety. We originally wanted the 18ft in the single-ended model, but when we finally went to pull the trigger they'd ditched that model the week prior, dang it.
Our motivators at the time were limited to weight, full bathroom, and club lounge.
Back then the weight difference was significant, now its only 300kg and unlike our previous tow veh your tow veh will be unaffected
The compromised combo bathroom in the earlier models is no longer the issue we faced, with the current 18 having a full bathroom.
The club lounge is good, but now we think that the cafe wouldn't be have been the deal-breaker we thought it might have been.
We opted to have the slide-out lounge deleted from our 20ft'er for a number of reasons (not limited to me not being a fan of them), so not having that in the 18fter wouldn't bother us at all. Im pretty confident we would have been almost equally as happy in the 18fter as we are with the 20fter. (and that just 1% less due to the rule, 'anything I own must, of course, must be the best')
The overall almost 1m body length of the 20ft over the 18ft seems excessive just to achieve what appears to be the half metre of wardrobe gained inside, and the $6500 price difference btw the two models is also difficult to find.
Our only real 100% no compromise deal-breaker in any van for us now would be the absence of a proper pantry, and the 18ft plan doesn't seem to have one so we'd struggle with that. We love the Expanda, but after 11 years of Expandas we are always considering our next step, and any van with no pantry is immediately poo poo'ed. The Jayco Adventurer has grown on us, but no pantry means no Adventurer.
Some other factors with a smaller van are easier towing and reversing, better fuel economy (particularly with the guzzling V8 Cruiser), more efficient for heating and cooling. Less ball weight on the already compromised Cruiser payload. I have a 20fter, so my loyalties lay there, but if your genuinely undecided there some pretty favourable factors tilted toward the 18