I use two 2" Suction cups, and they work fine for the thinwall PVC, about 5# max.
Also, the 1-1/4" exhaust extension should be below the pipe by about the distance off the pipe diameter, or, in my case 3". I have run my gennie 24 hours a day for up to five days.
The only problem I've ever had is the suction cups sun rotting.
2005 Georgetown 342DS XL, Full Banks Package
2005 Liberty Renegade 4X Toad
1989 Wrangler Sahara Toad
1984 19.5' Beachcraft i/o 5.o liter, 4-bbl (and you thought your Moho sucked gas!)
D/W Carole and Maggie the Teacup Lab (Black Chihuahua)