Axle question please

Hi all.
A friend of mine recently purchased a Viscount GT 20ft which the previous owner put a new full chassis and 4x4 suspension with 15 inch rims.
Whoever did the upgrade failed to check all clearances and on it's maiden trip with my mate had the tyre punt the wheelwell upwards forcing a vanity cupboard thru the ceiling and popping the roof, things like this happen when you hit a washout at 60kmh on Fraser Island.
Anyway the quick fixes are either [1] a set of axle bump stops or [2] fit the axles under the springs which would gain about 100mm as it has 9 leaf springs. The hard fix is a full set of new hangers and rocker mounts to gain the clearance.
What do you guys think, is it good engineering practice to under sling axles,would the RTA have any complaints, has anybody done this before.
All semi-trailer axles are underslung but i would imagine the stresses are different with the vans center axle position compared to a semi's rear position.

Any help would be appreciated.

Thanks Paul

I have done it before on a tandem caravan chassis that I converted to cart jetskis in crates, and now I use it to carry 4 quads on it as a flat deck trailer. I did it originally as the tyres protruded into the deck area of the chassis, and would have hit the jetskis in the crates. I underslung the axles, and also had to do an axle flip (overlay axles) to get enough height.

I have well and truly exceeded the weight limits of the axles on a few trips and have had no problems at all.

The thing to consider is it will change the height of the tow hitch, so the van may not ride level unless you have an adjustable hitch.

You'll find that a lot of Caravan manufacturers who sell an "Off-road" version are exactly that. The axle is slung under the springs, A/T tyres are fitted, and "Off-road" stickers are stuck on. So your mate shouldn't have any dramas with doing the same with the axle.

Thanks for the replies Guys, good point about the hitch height Surfin I will check if he has an adjustable one lying around when they get back from Canada.