wouldn't hurt if you're up to it. but would be easier to bring them inside once night temps drop into the 30's and setup some simple grow lights.

power strip/surge protector, pvc pipe or wooden stand to hold lights, plug in timer, either a 4' shop light or clamp on lamps with high wattage CFL's.

you can find some pics on the "growing under lights" and "orchids" and a few on the "tropical fruits" forums.

I am doing what houstontexas123 suggested. depending on the size of your tree determines what resources you will need, see pictures.

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the kumquat tree fits in side the 2 buckets as they appear. Both bucket are lined with aluminum foil. The upper bucket contain a 650 lumens 5300K TEMP CFL .bulb.

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16,- 1 gal broccoli plants with 8 CFL on for 16 hours/day of light for below and heat for the Meiwa kumquat tree's root base above. I have garden starts and a fortunella that is growing like a weed.

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Full picture with the lights on with the Meiwa plant still visible.

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bucket light over my Meiwa / fortunella tree. This is the complete setup.

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For smaller plants and trees you can see my 2 Nagami kumquat trees, 4 sweet lee tangerine trees and a cup full of sweet potato cuttings to root.

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Once the Meiwa tree / plant grows to a good size. she will sit under this light.

I too have a front porch I considered making a sun room with a glass roof. I decided to take the rout I did. Things are working out real well. When the tree is in it's 30 inch bow it will sit under the living room light. no mess or buckets. This should be in about 3 years. If you don't like it you can always start tomorrow

The problems I've had growing citrus indoors have been that the inside air is too dry - not that citrus need super high humidity, but they like levels that would cause mold to grow on walls in a normal house. And most often there isn't enough light, not bright enough and not long enough in the winter. Also, they tend to get buggy at some point during their winter vacation indoors. It's as if the plants are struggling to survive inside a house built for humans but the bugs that like to eat them love it.

Outside of building a greenhouse or sunroom (which I eventually did) the best thing I did was to cluster the plants together in a spare bedroom, put plastic sheeting down on the floor to protect the carpeting and allow me to mist the plants twice each day without damaging anything. I also hung clear plastic sheeting around the plant cluster to keep the humidity level higher around them but not against the walls and carpet. I put old floor lamps in and around them with strong lights on timers so that they got a lot of light for at least 6 hours each day. During two months of the winter (usually December and January) I would cool the room down (aiming for 40 degrees day and night), and turn off the supplemental lighting to let the plants go dormant. Most often they would lose most of their leaves. My goal was to save time and energy on their care and to promote blooming once I started watering and spritzing them again in February. I did lose some small trees but most of the time everyone responded well to the two month rest.

The problem with heating with hot water bottles out on your porch is that you will need to refill those bottles often during really cold nights. The colder the air the quicker that heat is going to dissipate.

You can provide a lot of heat with a small electric space heater (with a thermostat) if you tent the plant collection inside your sunroom porch.

This 4 ft by 4 ft by 3.5 ft tall box has a 25 deg. temperature rise with 20 CFL's of 13 watts each. It can hold 16 buckets of 5 gal each to grow peppers, egg plants, or citrus. Some thing like this would do fine in any room or on your porch in your zone.

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Click on image to open my display of other pics