I don't intend this post as hostile at all but for my money I would not put wheel spacers on a Trail 800 at all. (And haven't put them on mine)
The very reason for the Trail is to fit in truck boxes and fit on width restricted trails. I have encountered width restricted trails in Utah (Paiute Trails) and in places in British Columbia and if I'd had spacers I would be stopped at the 50" barrier posts while my ATV buddies would be able to carry on.
As to stability many people just look at a trail model and conclude "That's unstable". I can assure you I've been on more way off camber situations, often unexpectedly, and I tell you for a fact that at the very least a Trail model is much more resistant to a side flop than an ATV for instance.
If it's a search for ground clearance and the spacers are to make up for width loss following installing a lift kit, then like NMK says, it's not advised on a Trail.
I did go up a tire size and that worked out well, every half inch helps.
