I finally found a company selling plugs for the big holes behind the wheels. The parts fit really tight and seem to be high quality rubber. Hopefully I can keep some of the slush out of my frame this winter.
	
	
		
			
			
				
					
						
							
						
					
					www.frameplug.com
				
			
		
	
		
		
	
	
		
	
				
			
	
	