My general opinion on the IMS tanks is they are of poor quality and are porous. They leech fuel thru the plastic and stink up the garage and van. They also have ugly mould marks on them.
All this said, they do fit and hold fuel. Just don't expect the quality of the stock Acerbis-made tank. I'd rank them 1) Acerbis 2) Clarke and 3) IMS. Your KTM dealer should be able to get you an oversize Acerbis tank for the bike if you don't find it on Acerbis' web site. Clarke makes one too for it.
"Part # 1402 - New cap furnished, uses stock shrouds, mounts, and OEM petcock. Capacity: 3.5 gallons 13.2 Liters $170"
Thanks Tex. Now I wish I had gone with Clark! It actually looks like it fits better because it's a little smaller capacity. I've got the IMS on order and hope I'm not sorry. I have to wonder how they crammed another 2.2 gallons around the front of the KTM. I appreciate the advice on the leeching. If I decide to keep it, I'll make sure it's kept empty.
Unfortunately once the plasic is saturated it will still stink, even when empty.
If it were me and the extra capacity is not an issue, I'd send the IMS back and get the Clarke. I just put the Clarke 3.8 on my XR and am very pleased with it. The quality is definately there. No stink either.
When I say stink, I really mean it. I have a finished 12x24 work room in my garage since we live in a hot climate. When I'd work on the WR with the IMS I'd take the tank off and leave it in the main garage it stank so bad. If I left it in the workroom over night you could hardly breathe in there.
I just hauled the XR 3000 miles in the van with me. Other than the offgassing thru the vents they all do as you change altitude, the thing does not smell.
OK. I'm starting to hate this thing already and I haven't even seen it yet. So far 1) it STINKS, and 2) it needs a brazier! I wondered why they only show the '97 KTM in the White Bros catalog. I knew I should have gone with Clark! DOH!!!!! Klink you idiot!
Heck, I needed a larger tank in a hurry for this weekend. We're planning on doing some 50+ mile loops and I know how the 380 guzzles. I ruled out the EXC tank because I thought it was too expensive. About how much are they? I think I'll just put some plastic quart bottles of extra fuel in the rear fender pack for the ride.
As far as installation I set the Clarke and the Honda tank on the bench next to each other. The two mounts underneath bolted on, the petcock did, and the seat stabilizer screw at the back. It then slid right on the bike and uses the stock cap. Took all of 5 minutes to make the change.
Whatever you get, be sure and flush the tank out before you install it. Mine had some plastic scraps in it.
One more note, I truly believe the Clarke is superior to the IMS, but I got my Clarke for FREE... won it in a drawing from the Suzuki Nat'l Dual Sport Series.
Your fuel strap-on idea is a good one. You may also consider borrowing fuel from other guys on the trip. One way to do this on a 2 smoke is take a quart plastic oil container and put the correct amount of oil in it to make a gallon, then take raw gas a quart at a time from your 4 stroke friends. Fill it 4 times, shake the bike back and forth, and go ride. Be sure and put the first quart in with the oil, not dump the straight oil in the tank.