I'd strongly recommend going with an NMO magnet mount, if drilling a hole is out of the question. NMO gives you the most options for antennas down the road.
Avoid the cheap Chinese stuff. Stick with name brand.
I'm running both these antennas in different applications. Larsen and EMWave are both reputable companies that make good products and will stand behind them.
EM-M43002 Tri-Band IP67 Rated Roof Mount Antenna, 150-162/450-490/763-870 MHz
theantennafarm.com
150/450/700/800 Antenna, Gain (dB) Unity, 100 Watts, Whip Length 16.5"
theantennafarm.com
For the magnet mount base:
PCTEL Maxrad BGMSMAI NMO Magnet Mounts with SMA - Manufacturer: PCTEL Maxrad; Description: Magnetic Mount For use with NMO style antennas; Size: 2 3/8"; Model
theantennafarm.com
Avoid the Tram/Browning/Ham/Hobby grade stuff. Tram/Browning uses poorly installed coaxial connectors. You won't save any money if you have to replace cheap components.