AFAIK first the senate has to decide on the procedure for the vote, with only a simple majority required to vote through a proposed set of rules. So it's possible they could decide on a secret vote on impeachement, in which case there may be enough GOP senators willing to vote against Trump when the time comes.
Though it seems unlikely to me that any GOP senators would vote for a secret vote (as anybody who does is basically saying - yeah I might vote against)
I am expecting a whole raft of tricks / rules to be proposed and basically it will be pushed as far as possible to make the trial a GOP political stunt / rally
I expect something like the following to be happen - not sure which will get through but i suspect a fair few of them
1. Joe Biden and hunter Biden called to testify (and if they refuse the trial postponed whilst they very slowly... probably past the election) seek to force them through the courts
2. Witnesses and Jurors facing criminal prosecutions if they discuss the trial publicly whilst ongoing (also giving the pretext to say this has made the trial unfair) - basically stopping warren, sanders and biden talking about it ... though somehow trump will be allowed to tweet constantly
3. Further investigations as they will say the house investigations were incomplete - these will include background into ukraine corruption - so hunters job and his qualifications (quite probably expending out into china etc as well) , possibly even bringing Hillarys emails back into the mix
4. Politically motivated witch hunt - opening up a long and drawn out process of calling witness after witness to say this is all a political hit on the president
5. Dems basically allowed to call no witnesses
6. If proceedings start soon then dragging them out through the Iowa primary to keep sanders / warren stuck in DC (and biden if he is a witness)
7. Corruption allegations to be thrown at pretty much every senior democrat who was involved in the house proceedings
8. A narrative of Trump is draining the swamp and these people are trying anythinng to stop him fighting corruption ( yeah i know but it will play well with the Trump base)
9. The president of the Ukraine "volunteering" to be a trump witness (and possibly even announcing an investigation into the bidens when giving testimony)
10. Fox news basically saying its a democratic coup and next they will come for your guns and hopefully stopping short of saying the only good democrat is a dead democrat but knowing fox news they wont be far short of that
