Where on the plant are you taking cuts from?
In general, stems that are still soft and green are very hard to Clone, much harder than the woodier less fragile stems which in my experience is pretty much a sure thing.
Sounds like you need to disinfect your cutting trays properly... Buy new ones if you can afford it, get some hydrogen peroxide and disinfect the Clone Dome and all your tools.. I have found that letting the stems sit in a 3% h202 solution for a few min while you are taking all the cuttings helps dramatically with that rot you speak of.
Avoid spraying any nutrients on the leaves or into the tray, keep the rooter plug, rockwool, jiffies, moist at all times and don't let them dry out.
I have had the best success with an Rh of 90%... 100% seems to encourage mold spores to germinate and funky shit happens.
Make sure you are taking cuts near a node and not in the middle of the stem, through a node is also good.
Try not touch the cuttings again once they are in the Dome, place them and leave them be, just make sure there is moisture in the tray.
I have had success with no rooting hormone, and also success with rooting hormone... The gell worked well, but so do powders.... But so does nothing haha..
Keep the cutting size consistent at whatever you decide, and make sure they get a low intensity light... Cuttings outside is crazy in any weather as they will get dry very fast or transpire like mad and dry up if the sun hits them for too long.
The less you open the Dome, the less contaminants can get in, and if you disinfect properly when you are putting the cuts in the tent, then you should have a good success rate... And if cuts are failing to such a large degree, maybe try taking even more cuts!! Double to triple what you need, so that even in a disaster you should still get enough cuts out