Jacking should pose no problems. You should jack the trailer frame...never the axle. Block the uphill wheels, and secure the tongue, perhaps to the tow vehicle hitch, so that the trailer won't pivot off the jack.
You need to have a proper jack and good blocking to place under the jack. You also need a "high-lift" hydraulic bottle jack, because the jack travel must overcome both the suspension drop (for a tire change) and the additional 3" to 4" lift you desire.
But that's a lot of work every time you have to park the trailer after a trip.
I agree that the lumber platform(s) make more sense. What might work even better is to get some good gravel fill and some concrete pavers. Create a LEVEL pad on which to park the RV. No screwing around with planks or jacks.
It only needs to be large enough for the axle(s) and tires, but a permanent paver installation will be easier to back onto, and it won't rot. Also, lumber can be slippery when wet, whereas the pavers will have good traction, so your RV won't slide off. Use the gravel to create a "ramp" up to the paver parking area.
Best material is called "Crusher Run" with a gauge of about 1 1/2" for the largest pieces. Crusher run is a material that packs and drains well. It goes from "dust" sized particles to rocks up to about 1 1/2" across. The best stuff is limestone crusher run, but they make granite crusher run, too.
A local quarry or landscaping company can deliver a small dump truck load to your driveway, then you move it with a wheelbarrow. Get a "tamper" to pack the material as you put it in place. All you're doing is making a small "patio."
If you abandon this system, removing the pavers and gravel fill won't be a big chore.
While you're at it, plan for the trailer tongue. Will it need to be raised quite high to be level? If so, get a "
drop leg" for your tongue jack, and perhaps build a small platform for the jack using a old railroad tie. You may need to lift the tongue in stages. If so, a
second tongue jack that's removable could be helpful. This concept but with a clamp on mount might be useful. Use the main jack to lift, and use the second tongue jack to hold while you reset the main jack for more lift.
Any time you work on uneven ground and/or lift the tongue very high, you must use really good wheel chocks to ensure the trailer tongue won't pivot left or right...a potentially life-threatening move.
Don't forget landing pads for your stabilizer jacks. You can buy
stacks of plastic pads, and they are inexpensive. If you need real height on, say, one corner, get a decent concrete block and top it with a 2" x 6" board to distribute the load. If people are "living" in the parked RV, the stab jacks should be dropped for, well, stability. P.S. Don't try to "level" with stab jacks. You'll break or bend stuff.
Youroo!! 
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