there a very good idea.i made mine to save some cash,you can make sure you get all the rot and not just what failes the mot,i liked the idea that i could replace the whole part rather than stick another patch over the top there was 4 layers of steel on one of my outriggers,but dont roll it if your not commited,for mot mine needed a few small patches,after i got a good look at it i replaced all the jacking points all the outrigers,some chassis sections,4 of the top hat sections and both front and rear cross members, was worth it to no its all solid tho.
as for sinking in to the lawn, a gravel driveway wasent the best thing either ,a solid surface would be a big advantage.