Omni antennae recommendations

I am new here and to the Bai-cell product. I plan to set an omni antenna on top of a 20 foot pole on top of a fire tower. I did not want to put the radio that high for reasons of wind and impossibility to get at. The 2 questions I have are recommendations for an omni, and is 24 foot too far separation for the radio and if not recommendations for a cable?

For the omni antenna, we currently have an alpha but will be also trying a KP at our next site. It has to be dual pol and 45* slant so they are bigger than normal.

The run is only too long if you don’t have the cable for it. Calculate here: http://www.timesmicrowave.com/calculator/?
With an LMR 400 at 3.7 Ghz you are losing about 2.5 dB. You decide how much is too much.

Better cable costs more and is bigger/heavier.

What if you have to get to the omni? Same difference. You can always run the maintenance port down to a box in case you have to plug in, but I suspect you won’t.