foundation question

[Scot]

I am in the process of purchasing a triple wide manufactured home from champion. Initially the plan was to install the home on a concrete foundation, similar to a site built home. We just found out that my building site will require some very expensive methods to install the home because of access issues. We are discussing installing the home on concrete runners or on a system they called the "Magnum" which is designed for earthquake (we live in the Pacific NW, so earthquakes are a problem)

The Magnum system uses a steel post attached to an approximately 3 foot square concrete pad which is set on crushed rock, several of these Magnum supports are then used as the foundation for the home. The home is supposed to be able to move in an earthquake, absorbing the seismic energy.

I am wondering about the long term stability of setting the Magnum supports on the crushed rock as opposed to the concrete runners and also any other information about the relative merits of different foundations.

Additionally, we are planning to do a "pit set". The sales center is suggesting either using a concrete block material for the perimeter or a concrete board backed by pressure treated lumber. I am leaning toward the block material since I am not sure about wood being below ground level, even if it is pressure treated. Any information about this would be appreciated.

[Danny]

Scott,
i am not familiar witch the magnum system, but here in N.C. in some cases where a footing is very deep before hitting a good soil compaction , we add stone to the bottom of the footing to decrease concrete , so i would say it would work the same way...and be fine and then be great in case of an earthquake

[mac]

Ours is on a slab. At first we were going toward a conventional perimeter foundation and a rolled-on home, but learned that the factory hadn't actually done one of these yet, and balked (interesting...). Anyway, the slab with block skirting has worked out fine. We do live in earthquake country also (NW Oregon) but didn
t do the fancy foundation. I have thought about anchoring systems, though.
We thought about pit-set, but figured drainage might be an issue. So, instead, we backfilled around the home. So far (two years) all has been dry and pleasant. I wanted a full slab so critters couldn't tunnel under (we're out in the country).

[Eugene]

make sure this foundation will achor the home from wind and not heave from frost. The "Pit Set" idea sounds scarey, water needs to run away from the home on all 4 sides.