Bob my gso doesnt lose collimation even down low close to the horizon due to the fact that the gso 16 comes stock standard with 3 struts mine now has been modified with 6 struts to any movement that was there.
Without the mods i agree it was horendous to collimate because of the movement between the OTA and the UTA but i liked the design of the gso only because it will allow extra strut mods for stability.
Heres a link to the mods of the GSO 16
http://www.iceinspace.com.au/forum/s...light=makeover
Cheers Kev.