Early in 1993 I needed a simple 'Split Dipole' DE (seen above) to test several 2M Band yagi designs that I was working on....
For some 30 years it's been exposed to Devonshire weather (wind and rain/humidity etc), it's still going strong! So what are the secret ingredients?
Home constructors try to keep the water out, big mistake, you will see I have drilled two ventilation holes allowing the box to breath and dry out. Also on an annual basis spray in through the holes a generous squirt of GT85 (with PTFE) lubricant, penetrant and water displacer. Don't use silicon sprays, it can contaminate/damage electrical contacts, be warned!
Don't use end caps at the dipole ends, use flush mounting end plugs. Pretty looking end caps form a capacity hat, will detune and make wet weather performance worse!
Enthusiasts can very easily be caught up by dogma surrounding a particular mounting solution for the DE parts. There are also the mechanical issues, correctly supporting and sealing the coax feeder etc. It's important to look at the RF impact of any method. For example, the plastic box above will cause some shunt capacitance at the feedpoint along with dielectric losses. To mitigate a low Q design will suffer less and in all cases offers the best way forward.