Rust problems on 04 Symbol

Noticed rust stains on bottom of sills, just had a gander underneath the van, horrified at what I saw, Large rust holes in the nearside box section towards rear of van. Also rust setting in at many other places.
Probably too far gone to underseal, I was thinking of using an inhibitor such as Waxoyl

Anyone else out there had rust problems?, I'd be grateful for any tips on how you went about it

Hi Mike , only real way to cure is to weld in new metal to structural areas where holes exist then treat surface rust after wire brushing loose rust and dirt away,with an inhibitor such as bilt hamber or other rust converter . Paint converted surface with any gloss metal paint to protect then treat area with waxoyl underseal which does not harden and peel like horrible body schutz underseal which can hide serious rust then as you say inject all box sections and sills with a waxoyl type product or dinitrol through the various holes underneath also accessible via large removable grommets
   .  I would suggest a small traditional welders/  coachworks type place for best prices to make structure good , not motorhome main dealers! Thevrest can be done diy if you are fit and able.   Do not spray waxoyl and hope for the best as later on no one will touch underfloor areas soaked in waxoyl as it can burn like a good un especially if box sections are full  and you may end up with a damp free ash covered bodyshell and not a lot else! If you intend on keeping the van long term  act now and be bold as rust once it gets a good hold can be costly to fix if you cannot weld yourself.
        Campers and motorhomes retain value where an equivalent age van would probably have been scrapped by now so probably well worth spending a few quid now to secure vans future.

The Boxer van from 1995 into the mid noughties is very prone to rust like many others, including other Sevel vans, Ford VW and Mercedes if it has never been treated. On the Boxer/Ducato/Jumper the area around and below the battery, outriggers underneath, and the area below the water heater, sills etc. When buying an older 'van it pays to expect rampant rust, so have a good look before parting with any money and make sure the off side sill below the cascade or Henry water heater is as straight as. Usually the first place to suffer.

Hi, Sorry for a delayed response but have just returned from a holiday to Lisbon. We have a 2000 reg Symbol, purchased 4 years ago. Last year had to have a new sill welded on the drivers side due to extensive rust. The passenger side sill was not as bad and we had part of it replaced. The garage who ddid the repairs found that there had been a leak from the kitchen sink outlet house causing some rust to inside panels. A new hose was fitted. After the repairs the body was undersealed. Like you I was horrified when I first saw the amount of rust under the sills. 18 months later all looks well. We did not want an expensive job and although we had to keep checking the work being done as it took longer than we thought. At times were able to watch and talk to the welder as work was being carried out. The total cost £850.