No don't drill holes in the chassis, it will crack. All you can do is carry minimum gear & use lightweight gas bottle, that sort of stuff, unless you want to start removing interior bits like fridge etc.
the chassis are already loaded with large holes to keep the weight down..
leisure batteries.. less gas.. less food.. less junk.. no mover.. no shocks.. all ways to keep the weight down but the basic van structure is already paired down to a minimum.. not much hoper there..
So pleased the caravan was serviced today and everything was fine apart from the rubber on the inside of the windows that had popped out. Just cost £15 to get it replaced (all the 3 of them). Can't wait to get it on it's seasonal pitch. This is going to be our first year of not having to tow.
Buy a bigger car to tow your present van or down size your van to suit your present car.
Use glass fibre gas bottle get rid of toilet, shower and use site toilet block
Only use nudist sites, OH three outfits a day less weight x length of stay
buy food booze throw away Barbie etc from nearest supermarket when arrive on site, don't use an awning, get rid of battery go to bed at dusk get up at day break don't use EHU no cable.
You are not even supposed to drill holes in the 'A' frame to accommodate a leaf spring stabiliser because it weakens the structure so I can't imagine why anyone would even consider drilling holes in the chassis. I dread to think what an insurance company would think if a claim was ever made as the policy would most definitely be null and void. If you need a lighter unit then there must be a constructive reason for this which the real answer is to buy something more suitable or change to a better towcar.