The correct thing to do would be to get a Marine Utility Station License. 47CFR80.17(a)(5).
"Marine utility station.- A station in the maritime mobile service consisting of one or more handheld radiotelephone units licensed under a single authorization. Each unit is capable of operation while being hand-carried by an individual. The station operates under the rules applicable to ship stations when the unit is aboard a vessel, and under the rules applicable to private coast stations when the unit is on land."
Further more, under 47CFR80.37, Marine utility stations. One station license may be issued to authorize a designated maximum number of marine utility stations operating at temporary unspecified locations, normally in multiples of ten stations when:
(a) The licensee of each station is the same; and
(b) The authorized area of operation of each station is the same.
This way you could cover the unit in the trailer and as many handhelds as you want.
As a govermental public safety agency, you should be doing the right thing. If you are going to do the job, get the license, it is a piece of paper and a small fee and then you are covered and legal.