Do you have rust in, or out of the engine?
If inside (under the valve covers)...
Typically rust forms because the motor never reaches a temperature warm enough to boil the moisture out if the oil. Water laden oil will cause a light surface coating of rust that if left unattended to can cause more severe problems.
The easiest solution IMHO would be to buy an oil heater (they make a 115V magnetic one you can stick to the pan
http://www.northerntool.com/shop/tools/product_200339107_200339107?cm_ite=17151&cm_pla=Heaters%2C%20Stoves%20%2B%20Fireplaces%3EElectric%20Heaters&cm_cat=pricegrabber&cm_ven=Aggregates ) and dry the oil out, then add some Marvel oil to the crankcase oil and fire it up for a few to get the oil to coat all important surfaces. This should displace most of the water left on the bare iron parts and really slow the rusting process.
I normally use Marvel oil to "fog" the cylinders during a long lay-up to prevent cylinder rust, works killer.
My latest (last four) big blocks that were built for the jets have all been Glyptol coated on most of the bare iron surfaces, it really improves oil return and reduces oil foaming because of the smoother non porous surface and an added benefit is the lack of bare metal to impede surface rust from forming.
I have also used a regular electric heater and a few moving blankets to get the engine hot to dry engines out but have found the electric pan heaters to be way more effective.
Some will say it's not a big deal, but an oil analysis will prove otherwise.
Good luck!
