Junipers appreciate a soil that drains very freely, and they like to be kept on the slightly dry side. You can make a very good juniper soil from just fine gravel and pine bark. You can use the small gravel you buy in tubes at big box stores, but I suggest you screen it through insect screen and discard the sand or use it for something else (other than container soil). Mix at 2 parts gravel and 1 part bark. If you can find Turface, it would much improve the soil if you substitute 1 part of Turface for one of the parts of gravel. The plant will also appreciate it if you mix 1/3 cup of elemental sulfur into each cu ft of soil. Use a fertilizer with a 3:1:2 ratio, like MG 24-8-16 or 12-4-8.

You'll find you won't need to prune nearly as often as you suggest. They need all the sun they can get, so you'll need to rotate the plant regularly so the shaded side doesn't decline. Painting the lattice white would be marginally helpful as it would reflect more light to the 'back' of the plant.

Good luck - junipers aren't too fussy if you put them in a soil they like (not too soggy).

Al