like these antennas,they have a drain hole,but seal connections no need to let water in.besides ive seen drain holes freeze but above where it couples still let water in. Drain hole is best to expell condensationMost antennas are sealed "good enough" for typical/"normal" use. If you live in sort of 'worse' weather conditions then I'd certainly think about it. Sealing an antenna in the desert is not as probable as in a tropical environment. Can sealing an antenna be detrimental? Yes, it can be. Not very likely, but certainly possible. How do you tell if you should or not? Experience is the 'best' teacher'! Also the hardest.
I have a TRAM antenna I used on my truck for the longest time. The only reason I don't use it any more is that our ARES group was meeting at a hospital with an underground parking garage that has very low ceilings. The antenna was too tall so I went with a shorter Larsen.Good luck getting your questions answered about which connectors or coax to use.
Tram has a mediocre or less reputation.
I don't think DX Engineering, HRO, Universal, or Gigaparts need to start worrying about HD.