There are plenty of portable crank-up/tilt over towers out there. Just Google it. The price is pretty steep however. May I suggest that if you even have to question if you can build such a tower then you should not even attempt it. This is not something for someone to "see if he can build it" and there are so many things that can go wrong starting with material selection and ending with failed winches and improperly sized trailer to mount and transport it on. On top of all that 100 feet is a major undertaking even for an experienced welder and someone with tower building experience. For true portability something in the order of 50-70 feet, tilt over, freestanding and mounted on a trailer platform with outriggers is the way to go.