FNH, I don't think the donut idea will hurt you, but you could just as well put some loops of Poly type lines over the top section and let it rest against the larger part of the radiator. You would accomplish about same thing to guying the radiator with the donut.
Go back and read my post #20, where I talk about two guys I know that mounted their A99's on top of corrugated metal roofing. One was about 4' feet high above his 18' foot roof. Their antennas were dead in the shortest and longest directions that the metal ran.
One guy moved his antenna to the far end of the building near the edge, and saw improvement away from the building only. He ultimately got smart and moved his antenna to a tower on the ground out back, and then he was fine.
I'm in SE Texas, and I've been hearing Australia, New Zealand, and there abouts pretty regular for the last month or so, but they are not in there long, mostly in the mid morning, and late afternoon. From the way those guys I hear talking, there must be some pretty good traffic down there, and BTW I work a Starduster at 46' feet to the hub, and a Sirio Gain Master at 39' to the base, and I see first one then the other making the best contacts.
At my location my SD'r is the quietest by a good measure when conditions are moderately to really quite.
Good luck
