Our experience over the years with the topography in Region 2 has taught us one basic (and painful) truth regarding the use of HTs at Public Service Communication Events....
"HTs with Factory Stock Antennas, when operated at standing height, cannot be relied upon to always provide successful communications.

Handy-Talkies have 3 significant limitations:
1) 5 watts (max)
2) A Dummy Load / RF attenuating Stock Antenna
3) Antenna Height Above Ground

THE 3 PART SOLUTION
a) Use a Better-Than-Stock antenna
b) Increase the height of the better antenna above ground.
c) Add more power with a 25-30 watt amplifier.

You will find that the first two parts (a+b) will have a dramatic effect on your ability to communicate successfully.
- It is amazing what 5 watts on VHF and UHF will do when using: the right antenna, low-loss 1/2" coax, and a 20' mast.
See: ctaresregion2.org/forum/vhf-uhf-144-440-...st-tripod-antenna#78

However, where additional antenna height (with a "Better-Than-Stock Antenna") is not available and not going the distance, then MORE POWER is required and a 25 -30 watt amplifier (choice "c") will typically do the trick.
Examples:
Operating from a vehicle with an externally mounted antenna), or when operating from a fringe/shadowed location.

Another option:
Instead of using an HT and an Amplifier, consider this...
Get a Mobile Radio that has 5 - 50 watts (selectable), and have the power you need at your finger tips.